My guess is textbooks like English books or Greek Mythology might be ok...but math, science, computer, biology, etc. type textbooks will be miserable to use. Yes, I'm sure they will have wonderful animations or little video clips to show you how something works...but it's all about the note-taking needs to be perfected.
If you have ever had those types of scientific classes, your textbooks are all marked up. Not so much on the Emily Dickinson collection.
Actually, literature texts generally get marked up quite a bit. The biggest issue with handwritten annotations is that there's no easy way to connect everything. For example, read "Catcher in the Rye" and highlight allusions and references to light. Now piece all the instances together.
Where eBooks will be more interesting will be in liberal arts that employ a substantial amount of multimedia.
This announcement is taking place in an art museum, so let's use that as an example.
Art history textbooks would be a prime example of how a digital book with Internet connectivity would provide magnitudes of more information than a paper textbook. Due to printing costs and space, there is precious little room for photographic reproductions of paintings (the bulk of art history textbook photos are black-and-white due to cost), and even less for color plates. So in a typical undergraduate art survey class, any given artist might get a few pages in a massive textbook with a handful of B&W reproductions and if lucky, one color plate of a notable work. An eBook could link to Internet-based content so one could look at Rembrandt's entire work (including drawings) as well as a section of disputed works.
If I want to see a particular Rembrandt work, I should be able to see a virtual walkthrough of a gallery and see how it is currently being presented. Note that this also conveys scale. While art history books often list the dimensions of a given piece, it's not always easy to picture. In some instances it's hard to get close to the actual painting (perhaps it's hung high up on the wall) or there's a barrier (the glass case for the Mona Lisa is classic example, as well the glass protecting on of Michelangelo's sculpture of the Virgin Mary).
3D or video content would be even more invaluable for fields like sculpture, architecture, textiles, design, and performance art. Music, theater, dance, etc. would also benefit from multimedia content.
Even things like history books could access a vast repository of historic documents (photographs, maps, etc.).
Note that in these examples, the eBook with associated multimedia content needs to be viewed on a device that has a color screen, refreshes quickly, and has acceptable 3D performance.